Protein Molecular Weight Calculator Formula
Understand the math behind the protein molecular weight calculator. Each variable explained with a worked example.
Formulas Used
Estimated Molecular Weight
mw_da = residues * 110 + 18Estimated Molecular Weight
mw_kda = (residues * 110 + 18) / 1000Variables
| Variable | Description | Default |
|---|---|---|
residues | Number of Amino Acid Residues | 300 |
How It Works
Protein Molecular Weight Estimation
The molecular weight of a protein can be estimated from the number of amino acid residues using the average residue weight.
Formula
MW = N × 110 + 18
where N is the number of residues and 110 Da is the average amino acid residue weight (after peptide bond formation removes water). The +18 accounts for the water molecule completing the N-terminus and C-terminus. The actual average residue weight is 111.1 Da for a typical protein composition.
Worked Example
A protein with 300 amino acid residues.
residues = 300
- 01MW = 300 × 110 + 18 = 33,018 Da
- 02MW = 33.0 kDa
Ready to run the numbers?
Open Protein Molecular Weight Calculator